1. Field of the Invention
The present invention relates to a manipulator having an operating section including an end effector axis and one or more posture axes by which the orientation of the end effector axis is changed, together with a control method therefor. In particular, the present invention relates to a manipulator equipped with a compound mechanism for operating the end effector axis and the posture axes thereof, and to a control method for such a manipulator.
2. Description of the Related Art
In laparoscopic surgery, a number of small holes are opened in a patient's abdomen or the like, and an endoscope, a manipulator (or forceps), or the like is inserted, and surgery is carried out while the surgeon observes an image from the endoscope on a monitor. In this type of laparoscopic surgery, owing to the fact that opening of the abdominal cavity is unnecessary, the burden on the patient is small, and number of days required for the post-operative recovery and number of days spent in the hospital can be significantly reduced. Therefore, laparoscopic surgical operations are expected to find an increased range of applications.
On the other hand, manipulators used in laparoscopic surgery are desirably capable of quick and appropriate surgical techniques depending on the position and size of the affected region, and are used to perform various surgical techniques like suture, ligature, knot-tying and removing of the affected part of the patient. For this purpose, the present applicant has developed and proposed manipulators which have a high degree of freedom for manipulation and which can easily be operated (see, for example, Japanese Laid-Open Patent Publication No. 2002-102248 and Japanese Laid-Open Patent Publication No. 2004-301275).
With manipulators used for performing laparoscopic surgery, so as to enable various techniques to be performed, it is desirable for the posture of the end or tip of the end effector to possess a high degree of freedom. In this context, the provision of a compound mechanism for operating the end effector axis and the posture axes by which the orientation of the end effector axis is changed may be conceived of.
For example, in the event that the manipulator comprises the end effector axis and yaw and roll axes, wherein the respective axes are operated via wires, due to the fact that there is a mechanical relative influence therebetween, for operating either one of these axes, a compound mechanism is operated by operating two or more wires in a coordinated fashion.
Incidentally, as recognized by the present inventor, with this type of compound mechanism, when a torque is generated with respect to one axis, mechanically, an interference torque is generated on the other axes and on the actuator, such that unnecessary and wasted motion occurs at the other axis. In particular, in the case that the tip of the end effector grips a needle or a living body organism (hereinafter referred to also as a workpiece), or when shearing or the like is carried out, comparatively large torques are required, such that the collaterally generated interference torque becomes large, and unnecessary movement generated at the other axes easily arises. It is thought that such movements may also lead to cases where some sense of uneasiness is felt by the operator.
In order to prevent the generation of unnecessary movement by such interference torques, it is necessary to provide thick wires so as to obtain sufficient rigidity. However, when thick wires are used, it is required to make the longitudinal connecting portion through which the wire is inserted between the manipulator and the working unit large in diameter, and corresponding thereto, a need arises to set the holes, which are provided in the patient's abdomen or the like, to be quite large in size.